Drug Use in the Elderly

Abstract

Many changes in both pharmacokinetics and pharmacodynamics of several drugs have occurred as a result of physiologic alteration in the elderly. Decrease in total body water (due to decrease in muscle mass) and increase in total body fat affect volume of distribution. Thus, serum levels of water-soluble drugs such as lithium, aminoglycosides, alcohol and digoxin may go up due to decreased volume of distribution. Half-life of fat-soluble compounds such as diazepam, thiopental and trazadone may be increased because of the increase in body fat. The pharmacodynamics (what the drug dose to the body) of drugs may also be altered. For example, alcohol causes increase in drowsiness in older people more than in younger people at the same serum levels, and this is also true for fentanyl, diazepam, morphine and theophylline. In contrast, some drug effects are decreased, e.g., diminished heart rate (HR) response to isoproterenol and beta-blockers in the elderly.